closes #5669, increase the cachetable limit, it needs to be at least twice the size of the single pair that we have, otherwise, the evictor may sneak in when we are calling change_pair_attr, and catch the cachetable to have a size of 16, because we have added the new attr but not removed the old one

git-svn-id: file:///svn/toku/tokudb@50322 c7de825b-a66e-492c-adef-691d508d4ae1